It has been accepted practice to provide, in carburetor structures, a power fuel enrichment system comprised of a power valve assembly carried by the carburetor in a manner so as to be effected by engine manifold vacuum. The manifold vacuum acting on a movable pressure responsive member, which is adapted for operative engagement with the valving means of the power valve assembly, at idle or normal load conditions, as well as during engine deceleration is strong enough to overcome a spring resistance so as to maintain the valving means closed. When high power demands place a greater load on the engine and manifold vacuum drops below a predetermined value, the said spring overcomes the reduced vacuum thereby opening the valving means. Consequently, fuel flows through the open valve means and ultimately into the carburetor induction passage thereby enriching the otherwise normal fuel-air mixture. As engine demands are reduced manifold vacuum again increases. The increased vacuum acts on the pressure responsive member to finally overcome the resistance of the said spring thereby closing the valving means and shutting off the added supply of fuel which is no longer required.
The prior art has also suggested that such power valve assemblies be constructed so as to provide such additional fuel in distinct stages instead of providing a single increased rate of fuel flow in order to thereby more closely tailor the increase in fuel flow to the requirements of the engine.
However, heretofore, such multistage power valve assemblies have not been entirely successful because of certain undesirable characteristics. For example, the multistage power valve assemblies of the prior art have employed serially positioned valving members each of which coacted with serially situated valve seats. Usually such valve members were not positively guided during their movements toward and away from the valve seats thereby often creating a cocked position of the valve with respect to the seat.
Further, when such serially positioned valves were to be totally actuated, the opening force transmitted to the second valve would have to continually overcome a variable force of an intermediate spring situated between the first valve and a fixed spring seat. This increased the difficulty of attaining precise operating points with respect to which the second valve would open.
Further, because of governmentally imposed limitations on engine exhaust emissions and also governmentally imposed requirements for minimizing fuel consumption, the prior art power valve assemblies are found to be undesirable because the additional rates of fuel flow supplied thereby do not closely follow the actual increased rates of fuel flow required by the engine and instead usually exceed such additional fuel requirements.
Accordingly, the invention herein disclosed and claimed is primarily directed to the solution of the foregoing and other related and attendant problems of the prior art.